Perhaps since the invention of the wheel and certainly since the provision of supporting shafts and axles for carrying wheels, man has attempted to control the rate of rotation of the shaft and therefore the wheel by various frictionally engaging devices. Current conventional wisdom provides for a braking device that includes shoes or pads engaging portions of a rotating member in a frictional manner, in combination with a hydraulic or other means for selectively increasing the resistance to rotation, by the frictional engagement in which the rotating energy is transferred into heat. Such prior art devices can be characterized further in the fact that as a function of time, brake linings and the like wear out, surfaces subject to such frictional engagement may tend to warp, the characteristics of the frictional engagement also are sometimes associated with objectional noise, and in some cases the effectiveness of the brake can be compromised when wet, due to a change in the coefficient of friction.
The following U.S. Pat. Nos. reflect the state of the art of which applicant is aware, in so far as these patents appear to be germane to the instant process:
2,001,585 Roeder; 2,499,099 Kenyon; 2,548,919 Stevens et al.; 2,703,219 Henshaw; 3,026,974 Gouker; 3,033,322 Hughes; 3,503,473 Hackett.
Roeder teaches the use of a hydraulic brake in which pistons connected to a crank shaft provide resistance to the shaft rotation because the fluid within which the piston operates is incompressible. Appropriate valving is provided to control this resistance. FIG. 7 suggests the requisite use of brake linings as well.
Stevens and all teaches the use of a hydraulic brake in which frictional engagement between moving parts is required to effect stopping the engaging, areas appearing to be radially disposed about the rotating member.
Henshaw teaches the use of a safety lowering device in which cams disposed upon a shaft coact with piston like members disposed in cylinders having springs, but the true braking is based on the incompressibility of liquid disposed within the cylinder through opening and closing the appropriate valves.
Likewise, Gouker teaches the use of a vehicle brake in which opposed pistons have their motion retarded by means of fluid pressure communicating with piston heads in a cylinder, the fluid pressure altered by means of appropriate valving.
Hughes teaches the use of a braking and retarding apparatus in which a cylinder/piston arrangement provides braking on a rotating shaft by introducing fluid through appropriate valving into the cylinder area opposing motion of the piston somewhat similar to previously discussed references.
The patent to Hackett teaches the use of a fluid braking device in which a piston block includes spring portions, but the primary braking effect occurs by the incompressibility of the fluid and its associated control means, the spring section providing requisite back pressure.
The remaining reference shows the state of the art further.
By way of contrast, the instant application is directed to a device including an eccentric area on a shaft such as a crankshaft, pistons operatively connected thereto, cylinders surrounding the pistons, and plural springs having different spring rates in each cylinder area acting on a face of the piston remote from the shaft, and a means for changing the spring resistance as a function of the desire to control the shaft rotation. Thus, in an unfettered condition, the spring forces in each piston are provided in timed relation, one relative to another, such that any opposing spring force in one piston is offset and countermanded by an opposing spring force in another piston. However, when braking is desired, the spring tension on all springs is changed such that the piston meets substantially increased forces, the magnitude of which can be adjusted depending upon braking needs to retard shaft rotation. Means for changing the spring tension include associated instrumentalities for compressing or relaxing the spring as required.